alkenes and polymers Flashcards
which is stronger pi or sigma bond and why
sigma
between 2 nuclei
trans / E
opposite sides
cis / Z
same side
define electrophile
an electron deficient species with a vacant orbital often positively charged
define addition reaction
where one or more groups are added on to a molecule to give a single product
how can the stability of the carbocation intermediate be increased
methyl groups are weakly electro donating (compared to H) so the stability increases as the number of methyl groups attached to C+ increases
test for unsaturation/alkene
bromine water + ethene/propene
shake together/bubble gas through
orange bromine water decolourised
what is required for polymerisation
any short chain alkene
high pressure
peroxide initiator that produces free radicals
hydration of an alkene
steam + conc phosphoric acid
makes an alcohol
another test for an alkene
acidified potassium manganate
purple—> colourless
makes a DIol
hydrogenation of an alkene
use heat (above 150°) + nickel catalyst
add hydrogen
(forms an alkane)
order of stability of carbocations
primary<secondary<tertiary
which will be the main route of an asymmetrical electrophilic addition reaction
the more stable one
so secondary over primary
tertiary over secondary
4 features of a pi bond
2 areas of overlap (above and below nuclei)
parallel overlap
weaker than sigma
between 2 p orbitals
4 features of a sigma bond
single area of overlap (between 2 nuclei)
horizontal overlap
stronger than pi
between 2 p orbitals
define heterolytic bond fission
covalent bond between 2 species broken in an unequal manner
results in the bond pair of electrons being retained by one of the chemical species
the other does not retain any
one +ve charge product (an electrophile), one -ve charge
define homolytic bond fission
dissociation of a molecule where one electron is retained by each of the original fragments of the molecule.
two free radicals are obtained
as each chemical species retains one electron from the bond pair
define geometric isomerism
due to there being no free rotation about a C=C double bond (or in a ring structure) there are 2 different groups on each of the double bonded carbon atoms.
what properties do geometric isomers display
different physical properties
same chemical properties
how to decide if a compound is cis Z or trans E when it has all different groups attached
the atom with the highest atomic number takes priority
combustion of alkene/alkane method
burn one drop on a tuft of mineral wool on a heatproof matt
comparison of results for combustion of alkene/alkane
alkane- yellow luminous flame
alkene- sooty yellow luminous flame (incomplete combustion)
method of bromine water with alkene/alkane
1cm3 of bromine water in a test tube
add 3 drops of ane/ene
mix
comparison of results for alkene/alkane with bromine water
alkane- orange layer on top lower layer colourless (no reaction)
alkene- orange bromine water decolourised. upper layer of bromoalcohol
method of potassium manganate and dilute H2SO4 with alkene/alkane
2 drops KMnO4
1cm3 dilute H2SO4
few drops of ene/ane
shake at room temp
comparison of results for KMnO4 and H2SO4 for alkene/alkane
alkane- no change (no reaction)
alkane floats on top
alkene- pink->brown->colourless
alkene floats on top
method stability in water alkene/alkane
1cm3 distilled water
few drops of ene/ane
shake
comparison of results solubility in water alkene/alkane
alkane- 2 layers formed after shaking
organic layer on surface
alkene- 2 layers formal after shaking
organic layer on surface
cracking produces alkenes method
- 2-3cm3 medicicinal parafin onto mineral wool in a boiling tube
- set up apparatus
- Al2O3 is a catalyst
- heat catalyst (not mineral wool) continuously until bubbles appear
- discard first test tube (just hot air) then collect several tubes of gas
- remove delivery tube from water before cooling (to avoid suckback)
combustion test for alkene gas (after cracking)
hold test tube upside down + hold a flame to the mouth
produces a slight puff
apparatus for cracking
test tube with mineral wool + medicinal parafin and Al2O3 catalyst
delivery tube from this test tube into water trough
place test tube to collect gas into the water trough, over the delivery tube
alkene to bromoalcohol
aqueous Br2
alkene to alcohol
H2O gas (steam)
conc H3PO4
alkene to bromoalkane
HBr
alkene to dibromoalkane
Br2
alkene to diol
KMnO4
dilute H2SO4
purple -> colourless
alkene to alkane
(hydrogenation)
H2
Ni catalyst
150 degrees C
3 ways to reduce plastic waste
recycle
incinerate
chemical feedstock
how does recycling work
waste chopped into small peices
melted + moulded
how does incineration work
incinerate waste to produce chemicals
burn plastic produces heat energy
how does chemical feedstock work
plastic used as chemical feedstock
breaks down into polymers and rebuilds
